ox THE SYSTEMATIC POSITION OF SAGAKTIA LUCIvE. 729 



37. Note on the Systematic Position and Distribution of the 

 Actiniau Sagartia lucice. By J. Playfair McMurrich, 

 O.M.Z.S. 



[Received September 19, 1921 : Read October 18, 1921.] 

 (Text-figures 1-4.) 



During the last twenty years the small Actinian known as 

 Sagartia lucim has frequently been an object of study, and much 

 is known as to its variations, methods of reproduction, powers of 

 regeneration, reaction to light, locomotion, and general ecology. 

 As yet, however, it has not been subjected to an anatomical 

 investigation sufficientl}'^ detailed to reveal the features by which 

 its systematic position may be determined. 



It was first described in 1898 by V'errill, who gave a fairly 

 full description of its external form and coloration, without, 

 however, consideinng its anatomical structure. Later, Mrs. G. C. 

 Davenport (1903) in a study of the variations in the number and 

 arrangement of the vertical orange stripes, which are usually 

 such a chai'acteristic feature in the coloration of the column- 

 wall, showed that reproduction by longitudinal division or by 

 basal fragmentation was of frequent occurrence, variations in the 

 number of the orange stripes resulting therefrom, as well as 

 probably valuations in the arra,ngement of the mesenteries, which, 

 in the individuals with twelv^e stripes, were stated to be usually 

 arranged in twenty-four pairs. But still there was lacking a 

 sufficiently detailed account of the anatomy of the species to 

 determine definitely its systematic affiliations, and other papers 

 that have since dealt with it have not altered the situation in 

 this respect. It may be well, therefore, to put on record some 

 observations that were made several years ago, especially as they 

 led to interesting conclusions not only as to the systematic 

 position of the form, but also as to its distribution. 



Concerning the disk and tentacles little need be said, further 

 than to note the weakness of their musculature, the ectodermal 

 fibres of the tentacles forming a simple layer on the smooth, or 

 but slightly folded, surface of the mesogloea ; on the disk they 

 may even be absent. Between the bases of the outermost ten- 

 tacles and the apparent margin of the column there is a deep 

 fosse, which is vei-y characteristic of the species (text-fig. 1 ). It 

 is evidently equivalent to the thin portion of the column-wall that 

 intervenes in Meti-ldium senilis between the outermost tentacles 

 and the so-called collar, this latter being the upper edge of the 

 strong mesoglceal sphincter. But whereas in 3ietridiuin this 

 thin portion of the column is fully exposed in expansion, in 

 Sagartia lucice it remains introverted, thus producing the 

 characteristic fosse. The mesogloea forming its walls is very thin 

 and smooth on both surfaces, and both the endodei-m and ectoderm 



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